The cathode of a fuel cell utilizes pressurized charge air which is brought up to the fuel cell's operating pressure by an air compressor. During compression the air can become heated to a temperature of about 200° C. or higher, which is considerably higher than the operating temperature of the fuel cell. Therefore, a charge air cooler is used to cool the pressurized charge air to the desired temperature before it reaches the fuel cell stack; and before it reaches a humidifier that may be in-line between the air compressor and the fuel cell stack.
Conventional cathode thermal management systems use a liquid-to-air charge air cooler to remove heat from the charge air. The liquid coolant is typically water or a water-glycol mixture which is circulated through the fuel cell cooling system. The heat absorbed by the liquid coolant is subsequently rejected to the atmosphere through a heat exchanger, such as a radiator, in the front of the vehicle. The fuel cell engine itself also generates waste heat, which is low grade heat because of the relatively low stack operating temperature. This low grade heat rejection typically requires a relatively large radiator, and the added heat load from the charge air cooler that is rejected through this same radiator, forces a further increase in radiator size, to the point that the radiator may be difficult to package in the front space of the vehicle. Thus, the cooling of charge air places an additional load on the fuel cell's cooling system and complicates packaging in an already limited space. An example of such a prior art cathode thermal management system is illustrated in FIG. 1A.
Alternative approaches to cathode thermal management are needed in order to reduce the thermal load on the fuel cell cooling system, while ensuring that the charge air is cooled to an appropriate temperature. Furthermore, it is desired to reduce parasitic energy losses in the cooling of fuel cell engine.